Need cherry-pick #253 to release branch

[shonge]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do? If possible, provide a recipe for reproducing the error.
   Use tidb-lightning and set tidb-password

kn t1 logs -f lighting-tidb-lightning-qjtfs
flag provided but not defined: -tidb-password
Usage:
  -L string
        log level: info, debug, warn, error, fatal (default "info")
  -V    print version of lightning
  -backend string
        delivery backend ("importer" or "mysql")
  -c string
        (deprecated alias of -config)
  -config string
        tidb-lightning configuration file
  -d string
        Directory of the dump to import
  -importer string
        address (host:port) to connect to tikv-importer
  -log-file string
        log file path
  -pd-urls string
        PD endpoint address
  -server-mode
        start Lightning in server mode, wait for multiple tasks instead of starting immediately
  -status-addr string
        the Lightning server address
  -tidb-host string
        TiDB server host
  -tidb-port int
        TiDB server port (default 4000)
  -tidb-status int
        TiDB server status port (default 10080)
  -tidb-user string
        TiDB user name to connect
Failed to parse command flags:  flag provided but not defined: -tidb-password

2. What did you expect to see?
   Can set tidb-password

3. What did you see instead?
   Failed to parse command flags: flag provided but not defined: -tidb-password

4. Versions of the cluster

   • TiDB-Lightning version (run tidb-lightning -V):

     v3.0.8
     

   • TiKV-Importer version (run tikv-importer -V)

     (paste TiKV-Importer version here)
     

   • TiKV version (run tikv-server -V):

     (paste TiKV version here)
     

   • TiDB cluster version (execute SELECT tidb_version(); in a MySQL client):

     (paste TiDB cluster version here)
     

   • Other interesting information (system version, hardware config, etc):

5. Operation logs

   • Please upload tidb-lightning.log for TiDB-Lightning if possible
   • Please upload tikv-importer.log from TiKV-Importer if possible
   • Other interesting logs

6. Configuration of the cluster and the task

   • tidb-lightning.toml for TiDB-Lightning if possible
   • tikv-importer.toml for TiKV-Importer if possible
   • inventory.ini if deployed by Ansible

7. Screenshot/exported-PDF of Grafana dashboard or metrics' graph in Prometheus for TiDB-Lightning if possible

[kennytm]

The release branches have been synchronized and #253 will be included in v3.0.9.

[shonge]

Thank you.